Norovirus is the leading cause of viral gastroenteritis worldwide, and there are no approved vaccines or therapeutic treatments for chronic or severe norovirus infections. The structural characterisation of the norovirus protease and drug development has predominantly focused upon GI.1 noroviruses, despite most global outbreaks being caused by GII.4 noroviruses. Here, we determined the crystal structures of the GII.4 Sydney 2012 ligand-free norovirus protease at 2.79 Å and at 1.83 Å with a covalently bound high-affinity (IC50 = 0.37 µM) protease inhibitor (NV-004). We show that the active sites of the ligand-free protease structure are present in both open and closed conformations, as determined by their Arg112 side chain orientation. A comparative analysis of the ligand-free and ligand-bound protease structures reveals significant structural differences in the active site cleft and substrate-binding pockets when an inhibitor is covalently bound. We also report a second molecule of NV-004 non-covalently bound within the S4 substrate binding pocket via hydrophobic contacts and a water-mediated hydrogen bond. These new insights can guide structure-aided drug design against the GII.4 genogroup of noroviruses.
诺如病毒是全球病毒性肠胃炎的主要病因,目前还没有针对慢性或严重诺如病毒感染的批准疫苗或治疗方法。诺如病毒蛋白酶的结构表征和药物开发主要集中在 GI.1 诺如病毒上,尽管全球大多数疫情都是由 GII.4 诺如病毒引起的。在这里,我们测定了 GII.4 Sydney 2012 无配体诺如病毒蛋白酶在 2.79 Å 和与共价结合的高亲和力(IC50 = 0.37 µM)蛋白酶抑制剂(NV-004)在 1.83 Å 的晶体结构。我们发现,根据 Arg112 侧链的取向,不含配体的蛋白酶结构的活性位点既有开放构象,也有封闭构象。对无配体蛋白酶结构和配体结合蛋白酶结构的比较分析表明,当抑制剂共价结合时,活性位点裂隙和底物结合袋的结构存在显著差异。我们还报告了通过疏水接触和水介导的氢键在 S4 底物结合袋中非共价结合的第二个 NV-004 分子。这些新发现可以指导针对诺如病毒 GII.4 基因组的结构辅助药物设计。